The invention concerns method for the determination of two-dimensional work-area contours to monitor safe zones for numerically controlled lathes, whereby a safe zone is specified through determination of an axis-parallel segment contour of the workpiece and/or of the environment of the workpiece and a tool segment contour is defined for the portions of the tool including the tool support which are located on the side facing the safe zone and the work-area contour is calculated for a particular reference point of the tool segment contour.
Since collisions normally lead to substantial losses which can be caused both by repair costs as well as by down-time, it is advantageous to avoid these types of collisions through monitoring of the work process.
The use of sensors comprising, for example, one or more cameras for the purpose of collision monitoring is known in the art, the cameras being connected to an image analysis unit for prior recognition of collision events and the prevention thereof. Other sensors are used to determine the forces occurring in a lathe, in particular, at the tool and the tool support.
Image analysis has the disadvantage of being very difficult and therefore expensive and when forces are determined, collisions are first recognized after they have already occurred and have already possibly induced even minor damage.
Methods for the monitoring of collisions are known in the art which function without sensors by providing means for geometrical calculation of possible collision points which are then excluded during the work process. In this fashion, a working region is defined within which one must remain. The disadvantage of this procedure is the high amount of data which must be processed. This leads to large computing times which are prohibitive for online-monitoring unless sufficiently large computing power is available.
With lathes, this large amount of data can be substantially reduced since the lathe process can be largely described by two-dimensional calculations with the working area only being determined two-dimensionally. Despite this simplification, a large amount of data must nevertheless be processed so that online-monitoring is only possible with substantial computer power.
A digitizing method is known in the art from European laid-open publication EP 0 450 113 A1 with which the workpiece is sampled with a probe for recording geometrical data of three dimensional workpieces which are clamped to a machine, the workpiece surroundings also being sampled, with the probe sampled signals being utilized both for generating the workpiece geometrical data as well as to check for collisions with tools which, for their part, can likewise be sampled.
This method has the disadvantage that when utilized, for example, with a plurality of tools for processing a workpiece each change in a work tool requires a new sampling and new construction of a safe zone thereby causing substantial losses in time. Furthermore, the sampled values represent a particular situation which changes, for example, with a subsequent workpiece in the event that the position is even only slightly changed.
It would therefore be desirable to provide a method for the two-dimensional determination of work-area contours with which the work-area contour can be determined for collision monitoring using an acceptable amount of computer power, the method being safe and flexibly applicable.
This purpose is achieved in that at least the outer contour vertices of the safe zone and of the tool segment contour are determined and stored as coordinate values; in a monotonically increasing safe zone, each contour vertex of the safe zone is overlaid with each vertex of the tool segment contour and the coordinate value of the reference point is calculated for each overlay; and a work-area segment contour is determined in that those coordinate values which, when connected together, form a monotonically increasing segment contour, are sequentially chosen in the travel direction as vertex coordinates for the work-area segment contour.
In accordance with the invention, a safe zone is initially determined. The determination of the safe zone is carried-out through the definition of an axis-parallel segment contour which includes the contours of the workpiece and/or the environment of the workpiece. In addition, a segment contour is determined which describes the contour of the tool turret, e.g. the tool support including the tool and the tool holding means in the working position. In a subsequent step, the contour vertices as well as the safe zone and the tool segment contour are determined and stored as coordinate values. In order to determine an allowable work-area contour, the contour vertices of the safe zone and of the tool segment contour which were determined in the above manner are pairwise overlaid for each monotonic section assigned thereto and the coordinate values of a reference point are calculated for each overlay. Those coordinates are chosen from the coordinate values of each segment contour of a monotonic section of the safe zone which give a monotonic segment contour when combined with each other.
The invention has the advantage that a work-area is determined with little computing power within which the reference point must remain during the work process. In particular the work-area segment contour is determined through the pairwise overlay of the coordinate vertices of the safe zone and the tool segment contour using a small amount of processing data so that an online collision monitoring is facilitated without increased computer power.
In accordance with an advantageous embodiment of the invention, a travel direction is determined and the safe zone is subdivided into monotonically increasing and decreasing regions relative to this travel direction. The contour vertices are pairwise overlaid with the corresponding contour vertices of the monotonically increasing or decreasing sections of the tool segment contour for each of the monotonically increasing or decreasing regions of the safe zone and the coordinates of the reference point are calculated for each overlay. These coordinates are ordered in the travel direction for each monotonic section according to size and those coordinate points are chosen whose coordinate value in a direction perpendicular to the travel direction is larger than the previously chosen coordinate point. For monotonically decreasing sections, the points are chosen in the opposite travel direction.
In the event of a plurality of equal coordinate values in the travel direction, that coordinate point is chosen for the construction of the work-area contour which has the largest value in a direction perpendicular to the travel direction.
This embodiment of the invention allows for a straight-forward advantageous determination of the work-area in the various regions even for complex safe zone, or tool, and/or tool support shapes. The overall work-area or the overall work-area borders are defined through overlay of individual region borders.
In a further advantageous embodiment of the invention, the safe zone is calculated from the description of the components and from the structural data of the lathe. In this fashion the safe zone segment contour can be largely determined without additional data. The data which are in any event necessary for lathe processing are extracted from the component description, from the structural data, and are also used to describe the safe zone.
When running a processing program in a lathe, the tip of the tool is normally taken as the relevant reference point for processing. It is therefore also advantageous to take the tool tip as the reference point for the determination of the work-area.
In accordance with an additional advantageous configuration of the invention, the calculation of the borders of the work-area takes place during control initialization when calling the operation mode, following a change in the machine state, in the event of a tool change, or when changing tool corrections. The work-area borders are therefore always newly determined when any kind of change in the entire configuration takes place.
For processing of an NC-program, the automatic operation control advantageously checks each set of processing. instructions prior to execution as to whether or not the programmed path, i.e. the tool motion, remains within the work-area. When this is not the case, an error signal can then be issued prior to the beginning of the path feed motion. In contrast thereto, no error signal is issued for hand operation and the path feed motion is only allowed up to a work-area border.
The invention is described more closely below with reference to the figures .